It's supported on a number of exchanges, and fees are very low.

Let's say you wanted to move BTC from some exchange like KUCoin to another exchange where you can withdraw fiat, like Kraken, but the BTC on-chain fees happen to be high. What you could do is, on KUCoin, convert the BTC to LTC, and withdraw the LTC. That then is deposited on Kraken, and those LTC sold for fiat (e.g., USD). Voila, you moved the value from one exchange to another, and didn't use bitcoin to do it.

BitPay has support for Lightning network now, but many exchanges do not have LN support yet. So it might make sense that people are converting BTC to LTC for use in making a payment on BitPay. They aren't goitng long LTC (for more than a matter of minutes, at least), ... they are just using LTC as a payment rail.